This invention relates to siding panels suitable for surfacing exterior walls and roofs of buildings. While conventional siding panels produced from thermo-plastic such as polyvinylchloride (PVC) are well known and have been manufactured in many various shapes, difficulties have continued to be encountered due to the fact that satisfactory profile designs frequently are difficult or expensive to manufacture. It is difficult for instance to extrude wide, nonuniform, unsymetric profiles from thermoplastics. Complex dies are required to produce a product of acceptable tolerance from a well-mixed uniform extrudate which contains a minimum of internal stresses. Furthermore, exacting coordination between the downstream profile shaping equipment and die operation must be maintained to make marketable products. Hence, output from an extrusion process for complex profiles is significantly below the output for profiles of uniform, symetrical shape. Nonsymetrical shapes also increase the difficulty of laminating plastic film to siding panels. Conventional siding must also be installed by pressing each panel upwardly into place while the upper portion of the panel is nailed to the substrate. Conventional siding panels and panel assemblies of the type referred to above and which are subject to the disadvantages mentioned above include for instance those described in U.S. Pat. Nos. 3,473,274, 3,552,078, 3,520,099 etc.